code: def supported_cache_type(types):
      """Checks if link type config option consists only of valid values.
  
      Args:
          types (list/string): type(s) of links that dvc should try out.
      """
      if types is None:
          return None
      if isinstance(types, str):
          types = [typ.strip() for typ in types.split(",")]
  
      unsupported = set(types) - {
          "reflink",
          "hardlink",
          "symlink",
          "copy",
      }
      if unsupported:
          raise Invalid(
              "Unsupported cache type(s): {}".format(
                  ", ".join(unsupported)
              )
          )
  
      return types
  
file_path: dvc/dvc/config_schema.py
imports: import os
  from urllib.parse import urlparse
  from funcy import once, walk_values
  from voluptuous import REMOVE_EXTRA, All, Any, Coerce, Exclusive, Invalid, Lower, Optional, Range, Schema
  from dvc.log import logger
label_desc: Use image node_id 1 for calling a global function with example usage: supported_cache_type(types) and returns: types, None